This research will focus on chemical characterization and the mechanism of action of the heat-stable enterotoxins (STs) produced by porcine, bovine, and human strains of Enterotoxigenic (ENT plus) Escherichia coli. Each ST will be analyzed with respect to molecular weight, heat-stability, amino acid composition, amino and carboxyl-terminal residues and other chemical properties useful for comparative studies. The mechanism of action of various STs will be studied using the rat perfusion model to measure fluid and electrolyte fluxes and possible enzyme-mediated absorptive responses. Ion fluxes in isolated porcine intestinal epithelial strips will be studied. The association of radiolabeled ST to intestinal cells and intestinal membrane preparations will be examined. The nature of the receptor site(s) in the small intesitne for ST will be characterized and identified. Other work will look at the immunogenic properties of ST conjugated to bovine serum albumin and development of a rapid diagnostic test. The E. coli heat-labile enterotoxin will be purified to apparent homogeneity. The subunit structure will be characterized compared with cholera toxin. The mechanism of action will be studied using Y-l adrenal tumor cells and pigeon erythrocyte lysates. The interaction of radiolabeled LT with isolated intestinal cells and membrane preparations will be examined.